Caption: MMR vaccine. Assorted bottles of MMR vaccine. MMR is a vaccine which gives immunity to measles, mumps and rubella. It is generally given by injection to infants early in their second year. It contains dead or weakened forms of the viruses which cause each of the three diseases. The immune system in the body can easily deal with these weak forms. If the body is exposed to the virus again, it remembers the fastest way to deal with it. In this way, the virus is killed before any harm is done.